Wireless power transmission system and power transmission apparatus

ABSTRACT

A power transmission apparatus includes an inverter circuit, a power transmission antenna that wirelessly transmits alternating current power output from the inverter circuit, and a power transmission control circuit that causes the inverter circuit to output the alternating current power. The power transmission control circuit causes the inverter circuit to output the alternating current power as binary communication data by varying frequency of the alternating current power output from the inverter circuit between a first frequency and a second frequency, and performs amplitude control for eliminating a difference between amplitude of voltage of the alternating current power at a time when the frequency is the first frequency and amplitude of the voltage of the alternating current power at a time when the frequency is the second frequency.

BACKGROUND 1. Technical Field

The present invention relates to a wireless power transmission systemand a power transmission apparatus that wirelessly transmit power.

2. Description of the Related Art

During these years, wireless (noncontact) power transmission techniquesfor wirelessly (in a noncontact manner) transmitting power to mobiledevices such as mobile phones and electric vehicles are being developed.When power is transmitted in a wireless power transmission system,communication between a power transmission apparatus and a powerreception apparatus needs to be established for safety purposes.

Transmission of data from the power reception apparatus to the powertransmission apparatus is performed, for example, using a loadmodulation method, in which a value of a load is varied using switchingelements included in the power reception apparatus. By transmitting thevariation in the load to the power transmission apparatus, data can betransmitted. On the other hand, in an application (e.g., radio-frequencyidentification (RFID)) in which data needs to be transmitted from apower transmission side to a power reception side, data can betransmitted from the power transmission apparatus to the power receptionapparatus, for example, by modulating the frequency of power to betransmitted (hereinafter also referred to as “transmission power”).

Such data communication from a power reception apparatus to a powertransmission apparatus and data communication from a power transmissionapparatus to a power reception apparatus are disclosed, for example, inJapanese Unexamined Patent Application Publication No. 2011-211779 andJapanese Unexamined Patent Application Publication No. 2008-206305.

SUMMARY

In the existing art, however, while one of a power transmissionapparatus and a power reception apparatus is transmitting data to theother, it is difficult for the other transmit data to the one. Waitingtime is thus generated when bidirectional data communication isperformed, and it takes a long time to complete the communication.

In one general aspect, the techniques disclosed here feature a wirelesspower transmission system including a power transmission apparatusincluding an inverter circuit that converts first direct current powersupplied from a power supply into alternating current power and outputsthe alternating current power, a power transmission antenna thatwirelessly transmits the alternating current power output from theinverter circuit, and a power transmission control circuit that causesthe inverter circuit to output the alternating current power and outputsthe alternating current power as binary communication data by varyingfrequency of the alternating current power output from the invertercircuit between a first frequency and a second frequency, and a powerreception apparatus including a power reception antenna that receivesthe alternating current power wirelessly transmitted from the powertransmission antenna, and a power reception amplitude modulator thatvaries amplitude of voltage of the alternating current power input tothe power transmission antenna between a first amplitude and a secondamplitude. When transmitting first binary communication data to beoutput from the power transmission antenna to the power receptionantenna through electromagnetic coupling between the power transmissionantenna and the power reception antenna, the power transmission controlcircuit selects the first frequency as one of the first binarycommunication data and the second frequency as another of the firstbinary communication data. When transmitting second binary communicationdata from the power reception antenna to the power transmission antennathrough the electromagnetic coupling, the power reception amplitudemodulator selects the first amplitude as one of the second binarycommunication data and the second amplitude as another of the secondbinary communication data. The power transmission control circuitperforms, using the inverter circuit, amplitude control for eliminatinga difference between a third amplitude of the voltage of the alternatingcurrent power at a time when the frequency of the alternating currentpower is the first frequency and a fourth amplitude of the voltage ofthe alternating current power at a time when the frequency of thealternating current power is the second frequency.

According to the aspect of the present disclosure, the powertransmission apparatus and the power reception apparatus cansimultaneously transmit data bidirectionally, and time taken to completebidirectional communication can be reduced.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating an example of changes in the amplitudeof voltage at a time when a power transmission apparatus transmits Txdata according to embodiments of the present disclosure;

FIG. 1B is a diagram illustrating an example of transmission of Rx dataperformed by a power reception apparatus according to the embodiments ofthe present disclosure;

FIG. 1C is a diagram illustrating an example of a case where the powertransmission apparatus performs frequency modulation and the powerreception apparatus performs amplitude modulation at the same time;

FIG. 2 is a diagram illustrating the configuration of a wireless powertransmission system according to a first embodiment;

FIG. 3A is a diagram illustrating an example of the configuration of anamplitude modulator of a power reception circuit;

FIG. 3B is a diagram illustrating another example of the configurationof the amplitude modulator of the power reception circuit;

FIG. 4 is a diagram illustrating an example of an inverter circuit;

FIG. 5A is a diagram illustrating an example of waveforms of pulsesignals input to switching elements and an output voltage Va at a timewhen the amount of phase shift is 0 degree;

FIG. 5B is a diagram illustrating an example of the waveforms of thepulse signals input to the switching elements and the output voltage Vaat a time when the amount of phase shift is 90 degrees;

FIG. 6A is a diagram schematically illustrating a change in alternatingcurrent voltage (voltage of transmission power) input to a powertransmission antenna at a time when frequency is changed;

FIG. 6B is a diagram schematically illustrating a change in theamplitude of the voltage of transmission power at a time when an amountof phase shift between two pulse signals supplied to two switchingelements;

FIG. 6C is a diagram illustrating the amplitude of the voltage oftransmission power kept constant through amplitude control according tothe present embodiment;

FIG. 7A is a diagram illustrating an example of temporal changes in Txdata, Rx data, the frequency, the amount of phase shift, and the voltageof received power at a time when a power transmission apparatus istransmitting the Tx data to a power reception apparatus;

FIG. 7B is a diagram illustrating an example of temporal changes in Txdata, Rx data, the frequency, the amount of phase shift, and the voltageof transmission power at a time when the power reception apparatus istransmitting the Rx data to the power transmission apparatus;

FIG. 7C is a diagram illustrating an example of various waveforms at atime when a timing at which the power transmission apparatus transmitsTx data and a timing at which the power reception apparatus transmits Rxdata overlap;

FIG. 8 is a flowchart illustrating an example of operations of theamplitude control performed when the power transmission apparatustransmits Tx data to the power reception apparatus;

FIG. 9A is a diagram illustrating an example of a Tx signal (e.g., apacket signal) transmitted from the power transmission apparatus to thepower reception apparatus;

FIG. 9B is a diagram illustrating temporal changes in the Tx signal, thefrequency, the amplitude of the voltage of transmission power, and theamount of phase shift in a period defined by two broken linesillustrated in FIG. 9A;

FIG. 10 is a diagram illustrating the circuit configuration of aninverter circuit according to the present embodiment;

FIG. 11A is a diagram illustrating an example of waveforms of pulsesignals input to switching elements and the output voltage at a timewhen a duty ratio of each pulse signal is 0.5 (50%);

FIG. 11B is a diagram illustrating an example of waveforms of the pulsesignals input to the switching elements and the output voltage at a timewhen the duty ratio of each pulse signal is 0.25 (25%);

FIG. 12 is a flowchart illustrating an example of operations performedwhen Tx data is transmitted;

FIG. 13A is a diagram illustrating changes in the amplitude of voltageat a time when a power transmission side transmits Tx data to a powerreception side in the existing art;

FIG. 13B is a diagram illustrating an example of temporal changes in Txdata, Rx data, frequency, and a power reception coil voltage at a timewhen the Tx data is transmitted in the existing art;

FIG. 13C is a first diagram illustrating changes in the amplitude ofvoltage at a time when the power reception side transmits Rx data to thepower transmission side in the existing art;

FIG. 13D is a second diagram illustrating changes in the amplitude ofvoltage at a time when the power reception side transmits Rx data to thepower transmission side in the existing art;

FIG. 13E is a diagram illustrating an example of temporal changes in Txdata, Rx data, the frequency, and a power transmission coil voltage at atime when the Rx data is transmitted in the existing art;

FIG. 13F is a first diagram illustrating a problem caused when thetransmission of Tx data from the power transmission side to the powerreception side and the transmission of Rx data from the power receptionside to the power transmission side are simultaneously performed in theexisting art; and

FIG. 13G is a second diagram illustrating the problem caused when thetransmission of Tx data from the power transmission side to the powerreception side and the transmission of Rx data from the power receptionside to the power transmission side are simultaneously performed in theexisting art.

DETAILED DESCRIPTION

Underlying Knowledge Forming Basis of Present Disclosure

Underlying knowledge forming the basis of the present disclosure will bedescribed before describing embodiments of the present disclosure.

The present inventors have found that the following problem arises withexisting wireless power transmission systems described in the“Background Art” section.

The wireless power transmission systems disclosed in Japanese UnexaminedPatent Application Publication No. 2011-211779 and Japanese UnexaminedPatent Application Publication No. 2008-206305 wirelessly transmit powerbetween a power transmission coil (primary coil) and a power receptioncoil (secondary coil) through electromagnetic inductance. In thesesystems, data communication from a power reception side to a powertransmission side is performed by modulating a load in a power receptionapparatus. A power transmission apparatus can read data (hereinafteralso referred to as “Rx data”) transmitted from the power receptionapparatus by detecting changes in a waveform of a voltage at both endsof the power transmission coil caused by the modulation of the load. Onthe other hand, data communication from the power transmission side tothe power reception side is performed, for example, by modulating thefrequency of transmission power. The power reception apparatus can readdata (hereinafter also referred to as “Tx data”) transmitted from thepower transmission side by detecting changes in the frequency.

When a timing of the data transmission from the power reception side tothe power transmission side and a timing of the data transmission fromthe power transmission side to the power reception side overlap,however, the amplitude of the voltage of both ends of the powertransmission coil varies due to changes in the frequency and changes inthe load. In this case, it is difficult for the power transmissionapparatus to correctly demodulate Rx data. That is, there is a problemin that the systems disclosed in Japanese Unexamined Patent ApplicationPublication No. 2011-211779 and Japanese Unexamined Patent ApplicationPublication No. 2008-206305 can only perform half-duplex communication.

This problem will be described in more detail hereinafter with referenceto the drawings.

FIG. 13A is a diagram illustrating changes in the amplitude of voltageat a time when the power transmission side transmits Tx data to thepower reception side. A left-side diagram in FIG. 13A illustrates anexample of the waveform of the voltage of the power transmission coil(hereinafter also referred to as a “power transmission coil voltage”),and a right-side diagram in FIG. 13A illustrates an example of awaveform of a voltage at both ends of the power reception coil(hereinafter also referred to as a “power reception coil voltage”). Ineither diagram, a horizontal axis represents time, and this holds truein the following diagrams. In this example, a case is assumed in which avalue of the voltage at both ends of the power reception coil isproportional to a value of the voltage at both ends of the powertransmission coil.

FIG. 13B illustrates an example of temporal changes in Tx data, Rx data,frequency, and the power reception coil voltage in this case.

When transmitting binary data (Tx data) to the power receptionapparatus, the power transmission apparatus modulates the frequency ofpower to be transmitted (hereinafter also referred to as “transmissionpower frequency”) between f1 and f2. In the illustrated example, f1>f2,where f1 corresponds to data of “0” and f2 corresponds to data of “1”.As a result of the modulation of the frequency, the amplitude of thepower transmission coil voltage and the power reception coil voltagevaries. Since the power reception side does not transmit Rx data to thepower transmission side, the load on the power reception side remainsconstant in this example. Here, the amplitude of the power transmissioncoil voltage with the frequency f1 is denoted as V11, and the amplitudeof the power transmission coil voltage with the frequency f2 is denotedas V21. In addition, the power reception coil voltage corresponding tothe voltage V11 is denoted as V11′, and the power reception coil voltagecorresponding to the voltage V21 is denoted as V21′. The power receptionapparatus reads Tx data transmitted from the power transmissionapparatus by detecting changes in the frequency of transmittedalternating current power. That is, if the detected frequency is f1, thepower reception apparatus determines that Tx data is “0”, and if thedetected frequency is f2, the power reception apparatus determines thatTx data is “1”.

FIGS. 13C to 13E are diagrams illustrating transmission of Rx data fromthe power reception side to the power transmission side. FIG. 13Cillustrates an example of a waveform (left side) of the powertransmission coil voltage and a waveform (right side) of the powerreception coil voltage at a time when the transmission power frequencyis f1. FIG. 13D illustrates an example of a waveform (left side) of thepower transmission coil voltage and a waveform (right side) of the powerreception coil voltage at a time when the transmission power frequencyis f2. FIG. 13E illustrates an example of temporal changes in Tx data,Rx data, frequency, and the power transmission coil voltage in thiscase. In the example illustrated in FIG. 13E, the frequency is f2, butthe same holds when the frequency is f1.

When transmitting binary data (Rx data) to the power transmissionapparatus, the power reception apparatus modulates the amplitude of thevoltage of the power reception coil and the amplitude of the voltage ofthe power transmission coil by modulating the load in a circuit thereof.As illustrated in FIG. 13C, when the frequency is constant at f1, thepower reception apparatus varies the amplitude of the power receptioncoil voltage between V11′ and V12′ by modulating the load. The amplitudeof the power transmission coil voltage accordingly varies between V11and V12. The power transmission apparatus can read the Rx data bydetecting the variation in the amplitude.

On the other hand, as illustrated in FIG. 13D, when the frequency isconstant at f2, the power reception apparatus varies the amplitude ofthe power reception coil voltage between V21′ and V22′ by modulating theload. The amplitude of the power transmission coil voltage accordinglyvaries between V21 and V22. The power transmission apparatus can readthe Rx data by detecting the variation in the amplitude.

As described above, in the existing art, the power transmission sidetransmits data to the power reception side through frequency modulation,and the power reception side transmits data to the power transmissionside through amplitude modulation. It is difficult, however, tosimultaneously perform these data transmission operations. This pointwill be described hereinafter.

FIG. 13F is a diagram illustrating a problem caused when thetransmission of Tx data from the power transmission side to the powerreception side and the transmission of Rx data from the power receptionside to the power transmission side are simultaneously performed in theexisting art. When the power transmission apparatus modulates thefrequency between f1 and f2 in accordance with values of the Tx data,the amplitude of the power transmission coil voltage changes. At thistime, if the power reception apparatus modulates the load to transmitthe Rx data, the amplitude of the power transmission coil voltagefurther changes. When the transmission of Tx data and the transmissionof Rx data intermingle with each other, the amplitude of the powertransmission coil voltage varies between the four values V11, V12, V21,and V22. As a result, the Rx data might not be correctly demodulated onthe basis of changes in the amplitude of the power transmission coilvoltage.

FIG. 13G is a diagram illustrating an example in such a case. FIG. 13Gillustrates an example of temporal changes in, from top to bottom, Rxdata, Tx data, the power transmission coil voltage, a demodulated signalof the Rx data, the power reception coil voltage, and a demodulatedsignal of the Tx data.

The power transmission apparatus generates the demodulated signal of theRx data by comparing the amplitude of the power transmission coilvoltage with a certain threshold. The threshold is set as a valuebetween the amplitudes V11 and V12 with the frequency f1 or as a valuebetween the amplitudes V21 and V22 with the frequency f2. A value of thedemodulated signal of the Rx data becomes “0” when the amplitude of thepower transmission coil voltage is smaller than the threshold, and “1”when the amplitude of the voltage is equal to or larger than thethreshold.

In the example illustrated in FIG. 13G, the threshold is set as a valuebetween the amplitudes V21 and V22 with the frequency f2. The amplitudesV11 and V12 with the frequency f1 both fall below the threshold. In aperiod (inside an ellipse defined by a broken line in FIG. 13G) in whichthe amplitude is V12, therefore, the value of the demodulated signal ofthe Rx data is incorrectly determined as “0” (a solid line in thefigure), not as a correct value “1” (a broken line in the figure). Thatis, it is difficult to correctly demodulate the Rx data. It is to benoted that the same problem arises when the threshold is set as a valuebetween the amplitudes V11 and V12 with the frequency f1.

As described above, in the existing art, when the power transmissionside and the power reception side simultaneously transmit data, theamplitude of the power transmission coil voltage takes four values, andit is difficult to correctly demodulate the data by detecting theamplitude of the power transmission coil voltage.

With the configurations in the existing art, therefore, when either thepower transmission apparatus or the power reception apparatus istransmitting data, it is difficult for the other to transmit data. Insuch half-duplex communication, the power transmission apparatus and thepower reception apparatus need to withhold transmission of data untiltransmission of data from the other is completed. There is, therefore, aproblem in that it takes a long time to complete transmission ofinformation. In an application (e.g., a motor, an actuator, or the like)in which a control signal needs to be transmitted to a device on a powerreception side and a response signal needs to be obtained in real-timewhile power is being transmitted, in particular, a delay in datacommunication can pose a serious problem.

As a result of the above examination, the present inventors have arrivedat the following aspects of the present disclosure.

A wireless power transmission system according to an aspect of thepresent disclosure is a wireless power transmission system including

a power transmission apparatus including

an inverter circuit that converts first direct current power suppliedfrom a power supply into alternating current power and outputs thealternating current power,

a power transmission antenna that wirelessly transmits the alternatingcurrent power output from the inverter circuit, and

a power transmission control circuit that causes the inverter circuit tooutput the alternating current power and outputs the alternating currentpower as binary communication data by varying frequency of thealternating current power output from the inverter circuit between afirst frequency and a second frequency, and

a power reception apparatus including

a power reception antenna that receives the alternating current powerwirelessly transmitted from the power transmission antenna, and

a power reception amplitude modulator that varies amplitude of voltageof the alternating current power input to the power transmission antennabetween a first amplitude and a second amplitude,

in which, when transmitting first binary communication data to be outputfrom the power transmission antenna to the power reception antennathrough electromagnetic coupling between the power transmission antennaand the power reception antenna, the power transmission control circuitselects the first frequency as one of the first binary communicationdata and the second frequency as another of the first binarycommunication data,

in which, when transmitting second binary communication data from thepower reception antenna to the power transmission antenna through theelectromagnetic coupling, the power reception amplitude modulatorselects the first amplitude as one of the second binary communicationdata and the second amplitude as another of the second binarycommunication data, and

in which the power transmission control circuit performs, using theinverter circuit, amplitude control for eliminating a difference betweena third amplitude of the voltage of the alternating current power at atime when the frequency of the alternating current power is the firstfrequency and a fourth amplitude of the voltage of the alternatingcurrent power at a time when the frequency of the alternating currentpower is the second frequency.

According to the above aspect, the power transmission control circuitperforms, using the inverter circuit, the amplitude control foreliminating the difference between the third amplitude (V3) of thevoltage of the alternating current power at a time when the frequency ofthe alternating current power is the first frequency and the fourthamplitude (V4) of the voltage of the alternating current power at a timewhen the frequency of the alternating current power is the secondfrequency.

Since almost no difference is left between the amplitude (V3) of thevoltage of the alternating current power at a time when the frequency ofthe alternating current power is the first frequency (f1) and theamplitude (V4) of the voltage of the alternating current power at a timewhen the frequency of the alternating current power is the secondfrequency (f2) as a result of the amplitude control, an incorrectdetermination as in the existing art can be avoided. Even if either thepower transmission apparatus or the power reception apparatus istransmitting data, therefore, the other can transmit data at the sametime. It is to be noted that “eliminating a difference” does not meanthat the difference becomes exactly zero (0), but there may be a slightdifference.

A basic operation according to the embodiments of the present disclosurewill be described hereinafter with reference to FIGS. 1A to 1C.

FIG. 1A is a diagram illustrating an example of changes in the amplitudeof voltage at a time when Tx data is transmitted according to theembodiments of the present disclosure. A left-side diagram in FIG. 1Aillustrates an example of a waveform of the voltage of alternatingcurrent power input to a power transmission antenna (the same as avoltage at both ends of the power transmission antenna; hereinafter alsoreferred to as the “voltage of transmission power”), and a right-sidediagram in FIG. 1A illustrates an example of a waveform of the voltageof alternating current power output from a power reception antenna (thesame as a voltage at both ends of the power reception antenna;hereinafter also referred to as the “voltage of received power”).

As illustrated in the figure, a power transmission apparatus performsamplitude control for eliminating a difference between the amplitude V3of an alternating current voltage (hereinafter also referred to as a“voltage of transmission power”) input to the power transmission whenthe frequency is the first frequency (f1) and the amplitude V4 of thevoltage of transmission power at a time when the frequency is the secondfrequency (f2). The amplitude control is performed, for example, bycontrolling a plurality of switching elements included in an invertercircuit using a power transmission control circuit. More specifically,the amplitude control can be performed by adjusting, using a full-bridgeinverter circuit, a phase difference (also referred to as an “amount ofphase shift”) between two pulse signals supplied to two switchingelements that are simultaneously turned on (conductive state) among theplurality of switching elements. Alternatively, the amplitude controlcan be performed by adjusting a duty ratio of a pulse signal supplied toeach switching element. If the latter, that is, the duty control, isperformed, another inverter circuit, such as a half-bridge invertercircuit, may be used instead of a full-bridge inverter circuit.

As a result of the amplitude control, the amplitude of the voltage atboth ends of the power transmission antenna hardly changes (that is,V4≈V3) even if the frequency is changed between f1 and f2. Similarly,the amplitude of the voltage at both ends of the power reception antennahardly changes (V4′=V3′). Since the amplitude of the voltage oftransmission power hardly changes even if the frequency is modulated, Rxdata can be correctly demodulated on the basis of a comparison betweenthe amplitude of the voltage of transmission power and a certainthreshold even when the power reception apparatus transmits the Rx datawhile the power transmission apparatus is transmitting Tx data.

FIG. 1B is a diagram illustrating an example of transmission of Rx dataperformed by the power reception apparatus according to the embodimentsof the present disclosure. In this example, the frequency is fixed atf1. If an amplitude modulator of the power reception apparatus changesthe amplitude of the voltage of received power between V1′ and V2′ inaccordance with values of the Rx data, the power transmission powerdetects the changes, and the amplitude of the voltage of transmissionpower changes between V1 and V2. The power transmission apparatus candemodulate the Rx data by detecting the changes. In the embodiments ofthe present disclosure, the power transmission apparatus performs theabove amplitude control, and the amplitudes V1 and V2 when the frequencyis f0 become substantially the same as when the frequency is f1. As aresult, bidirectional communication becomes possible.

FIG. 1C illustrates an example of a case where the power transmissionapparatus performs frequency modulation and the power receptionapparatus performs amplitude modulation at the same time. In thisexample, when the power transmission apparatus selects the firstfrequency f1, the power reception apparatus selects the first amplitudeV1, and when the power transmission apparatus selects the secondfrequency f2, the power reception apparatus selects the second amplitudeV2. As a result of the amplitude control performed by the powertransmission apparatus, the amplitude of transmission power does notchange even if the frequency is changed between f1 and f2. A demodulatedsignal of Rx data, therefore, can be generated using the same thresholdregardless of whether the frequency is set to f1 or f2. Since Rx datacan be correctly demodulated while Tx data is being transmitted,transmission of Tx data and transmission of Rx data can besimultaneously performed.

More specific embodiments of the present disclosure will be describedhereinafter. In the following description, the same or correspondingcomponents are given the same reference numerals.

First Embodiment

FIG. 2 is a block diagram illustrating an example of the configurationof a wireless power transmission system according to a first embodimentof the present disclosure. The wireless power transmission systemaccording to the first embodiment includes a power transmissionapparatus and a power reception apparatus. The power transmissionapparatus includes a power transmission circuit 1000 that convertsdirect current (DC) energy (that is, DC power) input from an external DCpower supply 1030 into alternating current energy (that is, alternatingcurrent power) and that outputs the alternating current power and apower transmission antenna 1010 that transmits the alternating currentpower output from the power transmission circuit 1000. The powerreception apparatus includes a power reception antenna 1011 thatreceives the alternating current power transmitted from the powertransmission antenna 1010, a power reception circuit 1020 that convertsthe alternating current power received by the power reception antenna1011 into DC power and that outputs the DC power, and a load 1040 thatoperates on the DC power output from the power reception circuit 1020.

The power transmission antenna 1010 and the power reception antenna 1011can each be configured, for example, by a resonant circuit including acoil and a capacitor. Power is wirelessly transmitted through inductivecoupling (that is, magnetic field coupling) between the coils. Eachantenna may have a configuration with which power is wirelesslytransmitted through electric field coupling instead of magnetic fieldcoupling. In this case, each antenna can include two electrodes fortransmitting or receiving power and a resonant circuit including aninductor and a capacitor. A power transmission antenna and a powerreception antenna employing electric field coupling can be suitablyused, for example, when power is wirelessly transmitted to a mobiledevice such as a carrier robot in a factory.

The power reception apparatus can be, for example, the above-mentionedcarrier robot, a tip of a robot arm, a rotation unit of a monitoringcamera, or the like. The power transmission apparatus is an apparatusthat wirelessly supplies power to the power reception apparatus and canbe mounted, for example, at a root of the robot arm or a fixing unit ofthe monitoring camera. The load 1040 can be, for example, an imagecapture device, such as a charge-coupled device (CCD) camera, mounted onthe rotation unit of the monitoring camera or a device including amotor, such as an actuator mounted on the tip of the robot arm.

The power reception circuit 1020 includes a rectifier circuit(rectifier) 1021 that converts alternating current power output from thepower reception antenna 1011 into DC power and that supplies the DCpower to the load 1040, a power reception amplitude modulation circuit(power reception modulator) 1022 that modulates the amplitude of voltagein the power reception circuit and voltage in the power transmissioncircuit through load modulation, a frequency detection circuit(frequency detector) 1024 that detects the frequency of the transmittedalternating current power, a demodulation circuit (power receptiondemodulator) 1025 that demodulates a signal of Tx data transmitted fromthe power transmission circuit 1000 on the basis of the detectedfrequency, and a signal output circuit 1026 that outputs a controlsignal to the power reception amplitude modulator 1022 in accordancewith Rx data to be transmitted to the power transmission apparatus.

The power transmission circuit 1000 includes an inverter circuit 1001that converts DC power input from the DC power supply 1030 intoalternating current power using a plurality of switching elements, anamplitude detection circuit (amplitude detector) 1004 that detects theamplitude of an alternating current voltage input to the powertransmission antenna 1010, a demodulation circuit (power transmissiondemodulator) 1005 that demodulates an Rx signal transmitted from thepower reception circuit 1020 on the basis of the detected amplitude, apower transmission frequency modulator 1006 that determines a frequencyto be used in accordance with Tx data to be transmitted to the powerreception apparatus, a pulse output circuit 1002 that outputs pulsesignals for driving the plurality of switching elements included in theinverter circuit 1001, and a power transmission control circuit 1091that determines power transmission parameters on the basis of thefrequency determined by the power transmission frequency modulator 1006and that controls the pulse output circuit 1002. The power transmissionparameters are parameters for controlling timings at which the pluralityof switching elements included in the inverter circuit 1001 turn on(conductive state) and off (non-conductive state). The powertransmission parameters can include the frequency of a pulse signalinput to each switching element, a phase difference between two pulsesignals input to two switching elements that simultaneously turn onamong the plurality of switching elements, a duty ratio of the pulsesignal input to each switching element, and the like.

With this configuration, the wireless power transmission systemaccording to the present embodiment can communicate data bidirectionallythrough the power transmission antenna 1010 and the power receptionantenna 1011 while transmitting power. A supposed type of communicationdata can be, for example, a control signal (an instruction signalregarding a tilt, a pan, a zoom, and the like) for a monitoring cameraas a signal from a power transmission side to a power reception side. Asa signal from the power reception side to the power transmission side, asupposed type of communication data can be a response signal to aninstruction or image (video) data. In the case of a robot arm, asupposed type of communication data can be a control signal for a motorthat moves a robot or a response signal to it.

The components will be described in more detail hereinafter.

The power transmission control circuit 1091 performs control relating totransmission of power. For example, the power transmission controlcircuit 1091 determines the power transmission parameters including thefrequency of a gate pulse input to the inverter circuit on the basis ofinformation from the power transmission frequency modulator 1006 andcontrols the pulse on the basis of the parameters. The powertransmission control circuit 1091 can be, for example, an integratedcircuit including a processor such as a microcontroller (MCU). The powertransmission control circuit 1091 may be integrated with anothercomponent such as the pulse output circuit 1002 or the powertransmission frequency modulator 1006.

FIG. 3A is a diagram illustrating an example of the configuration of amodulator in the power reception circuit 1020. An illustrated modulator1022 a is a load modulation circuit connected between the powerreception antenna 1011 and the rectifier 1021. The modulator 1022 aincludes two switches and two capacitors connected parallel to the powerreception antenna 1011 and a resistor connected between a point betweenthe two capacitors and the ground. The modulator 1022 a performs loadmodulation by controlling open/close states of the two switches on thebasis of signals from the signal output circuit 1026. More specifically,the modulator 1022 a changes an overall load of the power receptionapparatus by switching on/off states of the two switches and opening orclosing a route of current different from a route to the load 1040. As aresult, information (Rx data) can be transmitted to the powertransmission apparatus.

Although the power reception amplitude modulator 1022 is arranged in aprevious stage of the rectifier 1021 in the example of the configurationillustrated in FIGS. 2 and 3A, the power reception amplitude modulator1022 may be arranged in a subsequent stage of the rectifier 1021,instead. FIG. 3B is a diagram illustrating an example of a modulator1022 b arranged in such a manner. The modulator 1022 b is connectedbetween the rectifier 1021 and the load 1040. The modulator 1022 bincludes a resistor and a switch connected parallel to the rectifier1021. The modulator 1022 b can change the overall load of the powerreception apparatus by switching an on/off state of the switch on thebasis of a signal from the signal output circuit 1026.

FIG. 4 is a diagram illustrating an example of the configuration of theinverter circuit 1001. The inverter circuit 1001 includes a plurality ofswitching elements S1 to S4 that change conductive/non-conductive statesin accordance with pulse signals supplied from the pulse output circuit1002. By changing the conductive/non-conductive state of each switchingelement, input DC power can be converted into alternating current power.In the example illustrated in FIG. 4, a full-bridge inverter circuitincluding the four switching elements S1 to S4 is used. In theillustrated example, each switching element is an insulated-gate bipolartransistor (IGBT), but a switching element of another type, such as ametal-oxide-semiconductor field-effect transistor (MOSFET), may be used,instead.

In the example illustrated in FIG. 4, among the four switching elementsS1 to S4, the switching elements S1 and S4 (first switching elementpair) output, when conductive, a voltage having the same polarity as aDC voltage supplied from the DC power supply 1030. On the other hand,the switching elements S2 and S3 (second switching element pair) output,when conductive, a voltage having an opposite polarity to the DC voltagesupplied from the DC power supply 1030. The pulse output circuit 1002supplies pulse signals to gates of the switching elements S1 to S4 inaccordance with an instruction from the power transmission controlcircuit 1091. At this time, the pulse output circuit 1002 performsamplitude control by adjusting a phase difference (also referred to asthe “amount of phase shift”) between the two pulse signals supplied tothe first switching element pair (S1 and S4) and a phase differencebetween the two pulse signals supplied to the second switching elementpair (S2 and S3).

FIGS. 5A and 5B are diagrams illustrating the amplitude control based onthe phase differences between the pulse signals. FIG. 5A schematicallyillustrates temporal changes in the four pulse signals and a voltage Vaoutput from the inverter circuit 1001 at a time when an amount φ ofphase shift between the two pulse signals supplied to the switchingelements S1 and S4 and an amount φ of phase shift between the two pulsesignals supplied to the switching elements S2 and S3 are 0 degree. FIG.5B schematically illustrates temporal changes in the pulse signals andthe voltage Va at a time when the amount φ of phase shift is 90 degrees.The amount φ of phase shift is adjusted by temporally shifting risingand falling timings of the pulse signals input to the switching elementsS3 and S4 relative to rising and falling timings of the pulse signalsinput to the switching elements S1 and S2. If the amount φ of phaseshift is changed, an output time ratio (a ratio of a period in which thevoltage Va is not zero to one cycle) changes. The output time ratio ofthe voltage Va becomes higher as the amount φ of phase shift becomescloser to 0 degree, and becomes lower as the amount φ of phase shiftbecomes closer to 180 degrees. The voltage Va output from the invertercircuit 1001 can be converted into a sine-wave voltage by a smoothingcircuit that is not illustrated and supplied to the power transmissionantenna 1010. The amplitude of the sine-wave voltage changes inaccordance with the output time ratio. By changing the amount φ of phaseshift, therefore, the amplitude of the alternating current voltage inputto the power transmission antenna 1010 can be changed.

Next, the amplitude control according to the present embodiment will bedescribed with reference to FIGS. 6A to 6C.

FIG. 6A is a diagram schematically illustrating a change in thealternating current voltage (voltage of transmission power) input to thepower transmission antenna 1010 at a time when frequency is changed. Inthe wireless power transmission system according to the presentembodiment, the amplitude of the voltage of transmission power becomessmaller as the frequency becomes higher as illustrated in FIG. 6A. Bychanging the frequency in order to transmit Tx data, therefore, theamplitude of the voltage of transmission power varies.

FIG. 6B is a diagram schematically illustrating a change in theamplitude of the voltage of transmission power at a time when the amountφ of phase shift between two pulse signals supplied to two switchingelements is changed. If the amount φ of phase shift is changed, theoutput time ratio of the voltage Va output from the inverter circuit1001 changes due to the above-described principle. The amplitude of thealternating current voltage (e.g., sine-wave voltage) input to the powertransmission antenna 1010 accordingly changes. The amplitude of thevoltage of transmission power becomes largest when the amount of phaseshift is 0 degree, and becomes smaller as the amount of phase shiftbecomes closer to 180 degrees.

That is, when a relationship between the amplitude of the voltage oftransmission power, the frequency, and the amount of phase shift is asillustrated in FIGS. 6A and 6B, control can be performed in such a wayas to keep the voltage of transmission power constant by appropriatelyselecting the two parameters, namely the frequency and the amount ofphase shift.

FIG. 6C is a diagram illustrating the amplitude of the voltage oftransmission power kept constant through the amplitude control accordingto the present embodiment. FIG. 6C illustrates a curve (solid line)representing a relationship between the amplitude of the voltage oftransmission power and the frequency at a time when the amount φ ofphase shift is φ1 and a curve (broken line) representing a relationshipbetween the amplitude of the voltage of transmission power and thefrequency at a time when the amount φ of phase shift is φ2 (>φ1). Theamplitude of the voltage of transmission power when the frequency is f1and the amount of phase shift is φ1 (a point P1 in FIG. 6C) and theamplitude of the voltage of transmission power when the frequency f isf2 (<f1) and the amount φ of phase shift is φ2 (a point P2 in FIG. 6C)are the same. That is, when the frequency is modulated between f1 andf2, the amplitude of the voltage of transmission power can be keptconstant by modulating the amount of phase shift between φ1 and φ2.

The power transmission control circuit 1091 according to the presentembodiment, therefore, varies the frequency between f1 and f2 and theamount of phase shift between φ1 and φ2 when transmitting data (Tx data)to the power reception apparatus. Since the amplitude of the voltage oftransmission power corresponding to the frequency f1 and the amount φ1of phase shift is the same as the amplitude of the voltage oftransmission power corresponding to the frequency f2 and the amount φ2of phase shift, transmission of Tx data and reception of Rx data can besimultaneously performed unlike in the existing art.

The transmission of Tx data, the transmission of Rx data, and theoperation for simultaneously transmitting Tx data and Rx data accordingto the present embodiment will be described hereinafter with referenceto FIGS. 7A to 7C.

FIG. 7A is a diagram illustrating an example of temporal changes in Txdata, Rx data, the frequency, the amount of phase shift, and the voltageof received power at a time when the power transmission apparatus istransmitting the Tx data to the power reception apparatus. When only thepower transmission apparatus is transmitting the Tx data to the powerreception apparatus, the Rx data is in a no-signal state. The powertransmission control circuit 1091 changes the frequency in accordancewith binary values of the Tx data transmitted from the powertransmission apparatus to the power reception apparatus. At this time,correction based on the amount of phase shift is also performed. Morespecifically, when the Tx data is “0”, the power transmission controlcircuit 1091 sets the frequency to f1 and the amount of phase shift toφ1. When the Tx data is “1”, on the other hand, the power transmissioncontrol circuit 1091 sets the frequency to f2 and the amount of phaseshift to φ2. As a result of this control operation, the amplitude of thevoltage of received power is kept constant regardless of the signalvalue of the Tx data. The frequency detector 1024 and the powerreception demodulator 1025 of the power reception apparatus can detectthe frequency of transmitted high-frequency power and demodulate thesignal of the Tx data.

FIG. 7B is a diagram illustrating an example of temporal changes in Txdata, Rx data, the frequency, the amount of phase shift, and the voltageof transmission power at a time when the power reception apparatus istransmitting the Rx data to the power transmission apparatus. When onlythe power reception apparatus is transmitting the Rx data to the powertransmission data, the Tx data is in a no-signal state. The signaloutput circuit 1026 modulates the load in the power reception amplitudemodulator 1022 and the amplitude of the voltage input to the powertransmission antenna in accordance with binary values of the Rx datatransmitted from the power reception apparatus to the power transmissionapparatus. The amplitude detector 1004 and the power transmissiondemodulator 1005 of the power transmission apparatus can demodulate theRx data by detecting this change in the amplitude.

FIG. 7C is a diagram illustrating an example of various waveforms at atime when a timing at which the power transmission apparatus transmitsTx data and a timing at which the power reception apparatus transmits Rxdata overlap. FIG. 7C illustrates an example of temporal changes in,from top to bottom, the Rx data, the Tx data, the voltage oftransmission power, a demodulated signal of the Rx data, the voltage ofreceived power, and a demodulated signal of the Tx data. Even when thetransmission of the Tx data and the Rx data overlaps, the amplitudedetector 1004 and the power transmission demodulator 1005 of the powertransmission apparatus can demodulate the Rx data from the powerreception apparatus on the basis of a comparison between the amplitudeof the voltage of transmission power and a certain threshold. Inaddition, the frequency detector 1024 and the power receptiondemodulator 1025 of the power reception apparatus can demodulate the Txdata from the power transmission apparatus by detecting the changes inthe frequency of the voltage of received power.

As described above, unlike in the existing art, since the amplitude ofvoltage is kept constant even while Tx data is being transmitted in thepresent embodiment, interference can be prevented even if Rx data issimultaneously transmitted from the power reception apparatus. Accordingto the present embodiment, even if the power transmission apparatus andthe power reception apparatus simultaneously transmit data, signals fromthese apparatuses can be detected without a loss. As a result, the powertransmission apparatus and the power reception apparatus need notwithhold transmission of data until transmission of data from the otherapparatus is completed, and a communication capacity improves.

Next, the amplitude control performed by the power transmissionapparatus according to the present embodiment will be described morespecifically.

The amount of change in the amplitude caused when the frequency ischanged might differ depending on a value of the load connected to thepower reception circuit 1020. In this case, the power transmissioncircuit 1000 may monitor the voltage of transmission power whiletransmitting Tx data, and perform feedback control such that theamplitude of the voltage after the frequency is changed becomes the sameas the amplitude of the voltage before the frequency is changed. As aresult, even if the value of the load varies, the amplitude of thevoltage of transmission power can be kept at a constant value. Inaddition, in order to accommodate a plurality of types of loads, a tablespecifying correspondences between the frequency and the amount of phaseshift in accordance with the load may be prepared and stored in a memory1092.

FIG. 8 is a flowchart illustrating an example of operations of theamplitude control performed when the power transmission apparatustransmits Tx data to the power reception apparatus.

First, the amplitude detector 1004 measures the amplitude of a voltage(voltage of transmission power) input to the power transmission antenna1010 (step S101). Next, the power transmission control circuit 1091changes the frequency of transmission power in accordance with a valueof data to be transmitted (step S102). After the frequency is changed,the amplitude detector 1004 again measures the amplitude of the voltageof transmission power (step S103). The measured values of the amplitudeof the voltage of transmission power before and after the frequency ischanged are transmitted to the power transmission control circuit 1091.The power transmission control circuit 1091 determines whether theamplitude of the voltage of transmission power after the frequency ischanged is equal to the amplitude of the voltage of transmission powerbefore the frequency is changed (step S104). If the amplitude after thefrequency is changed is not equal to the amplitude before the frequencyis changed, the amount of phase shift is changed in steps of a certainvalue and repeats the measurement of the amplitude of the voltage oftransmission power (step S103) until the amplitude after the frequencyis changed becomes equal to the amplitude before the frequency ischanged (step S105). When the measured amplitude has become equal to theamplitude before the frequency is changed, the power transmissioncontrol circuit 1091 saves the amount of phase shift at this time to thememory 1092 (step S106). In doing so, if the frequency is changed nexttime, the amount of phase shift can immediately enter, using the valuesaved in the memory 1092, a state in which the amplitude becomesconstant.

FIG. 9A is a diagram illustrating an example of a Tx signal (e.g., apacket signal) transmitted from the power transmission apparatus to thepower reception apparatus. FIG. 9B is a diagram illustrating temporalchanges in the Tx signal, the frequency, the amplitude of the voltage oftransmission power, and the amount of phase shift in a period defined bytwo broken lines illustrated in FIG. 9A. When a first signal of a packetis transmitted, the power transmission control circuit 1091 changes thefrequency, and the amplitude of the voltage of transmission powerchanges. The power transmission control circuit 1091 adjusts the amountof phase shift through the operations illustrated in FIG. 8 so that thechange becomes smaller. As a result, the amplitude of the voltage oftransmission power becomes the same as the amplitude before thefrequency is changed. The amount of phase shift at this time is saved tothe memory 1092, and the amount of phase shift can be changed next timeand later by referring to the value stored in the memory 1092. As aresult of these operations, time taken to reset the amplitude of thevoltage of transmission power to a state before the frequency is changedcan be reduced, and the amplitude of the voltage of transmission powercan always be kept constant.

Second Embodiment

Next, a second embodiment of the present disclosure will be described.In the present embodiment, not the full-bridge inverter circuit 1001illustrated in FIG. 4 but a half-bridge inverter circuit is used. Theamplitude of voltage, therefore, is controlled not through the phasecontrol according to the first embodiment but by controlling a dutyratio of a pulse signal input to each switching element. Other pointsare the same as in the first embodiment. Differences from the firstembodiment will be described hereinafter.

FIG. 10 is a diagram illustrating the circuit configuration of aninverter circuit 1001 a according to the present embodiment. Theinverter circuit 1001 a is a half-bridge inverter circuit including twoswitching elements S1 and S2 and two capacitors. The two switchingelements S1 and S2 and two capacitors C1 and C2 are connected parallelto each other. An end of the power transmission antenna 1010 isconnected to a point between the two switching elements S1 and S2, andanother end is connected to a point between the two capacitors C1 andC2.

The power transmission control circuit 1091 and the pulse output circuit1002 supply a pulse signal to each switching element such that theswitching elements S1 and S2 alternately turn on. As a result, DC poweris converted into alternating current power.

Since the number of switching elements is 2, the phase control describedin the first embodiment is not applied in the present embodiment. Thepower transmission control circuit 1091 according to the presentembodiment, therefore, adjusts the output time ratio of the outputvoltage Va by adjusting the duty ratio (that is, a ratio of a period inwhich the pulse signal is on to one cycle) of each pulse signal. As aresult, the amplitude of the voltage of alternating current power inputto the power transmission antenna 1010 is adjusted.

FIGS. 11A and 11B are diagrams illustrating the duty control accordingto the present embodiment. FIG. 11A illustrates an example of the pulsesignals input to switching elements S1 and S2 and the output voltage Vaat a time when the duty ratio of each pulse signal is 0.5 (50%). FIG.11B illustrates an example of waveforms of the pulse signals input tothe switching elements S1 and S2 and the output voltage Va at a timewhen the duty ratio of each pulse signal is 0.25 (25%). As illustratedin the figure, by changing the duty ratio, the output time ratio (thatis, a period in which the voltage Va is not zero to one cycle) of thevoltage Va can be changed. As a result, the amplitude of the smoothedvoltage of transmission power, too, can be changed. Such pulse signalswhose duty ratios are different from each other are generated, forexample, by the pulse output circuit 1002 including a pulse-widthmodulation (PWM) control circuit. The duty ratio is adjusted within arange of 0% to 50%. When the duty ratio is 50%, the amplitude of thevoltage of transmission power becomes largest, and when the duty ratiois 0%, the amplitude of the voltage of transmission power becomessmallest.

When transmitting Tx data to the power reception apparatus, the powertransmission control circuit 1091 according to the present embodimentchanges the duty ratio in accordance with the modulation of thefrequency. More specifically, when decreasing the frequency, the powertransmission control circuit 1091 increases the duty ratio, and whenincreasing the frequency, the power transmission control circuit 1091decreases the duty ratio.

FIG. 12 is a flowchart illustrating an example of operations performedwhen Tx data is transmitted according to the present embodiment.Operations in step S101 to S104 are the same as those in steps S101 toS104 illustrated in FIG. 8, respectively, and description thereof isomitted. If, in step S104, the measured amplitude is not equal to theamplitude before the frequency is changed, the power transmissioncontrol circuit 1091 changes the duty ratio of each pulse signal by acertain value (step S205). The power transmission control circuit 1091then repeats the operations in steps S103, S104, and S205 until themeasured amplitude becomes equal to the amplitude before the frequencyis changed. When the measured amplitude has become equal to theamplitude before the frequency is changed, the power transmissioncontrol circuit 1091 saves information regarding the duty ratio at thistime to the memory (step S206).

As a result of the above operations, as in the first embodiment, theamplitude of the voltage can be kept constant even if the frequency ischanged. Even when the power reception apparatus simultaneouslytransmits Rx data, therefore, the Rx data can be correctly demodulatedon the basis of the amplitude of the voltage of transmission power.

The duty control according to the present embodiment can also be appliedto a case where the full-bridge inverter circuit according to the firstembodiment is used.

As described above, the present disclosure includes wireless powertransmission systems and a power transmission apparatus described in thefollowing items.

Item 1

A wireless power transmission system including

a power transmission apparatus including

an inverter circuit that converts first direct current power suppliedfrom a power supply into alternating current power and outputs thealternating current power,

a power transmission antenna that wirelessly transmits the alternatingcurrent power output from the inverter circuit, and

a power transmission control circuit that causes the inverter circuit tooutput the alternating current power and outputs the alternating currentpower as binary communication data by varying frequency of thealternating current power output from the inverter circuit between afirst frequency and a second frequency; and

a power reception apparatus including

a power reception antenna that receives the alternating current powerwirelessly transmitted from the power transmission antenna, and

a power reception amplitude modulator that varies amplitude of voltageof the alternating current power input to the power transmission antennabetween a first amplitude and a second amplitude,

in which, when transmitting first binary communication data to be outputfrom the power transmission antenna to the power reception antennathrough electromagnetic coupling between the power transmission antennaand the power reception antenna, the power transmission control circuitselects the first frequency as one of the first binary communicationdata and the second frequency as another of the first binarycommunication data,

in which, when transmitting second binary communication data from thepower reception antenna to the power transmission antenna through theelectromagnetic coupling, the power reception amplitude modulatorselects the first amplitude as one of the second binary communicationdata and the second amplitude as another of the second binarycommunication data, and

in which the power transmission control circuit performs, using theinverter circuit, amplitude control for eliminating a difference betweena third amplitude of the voltage of the alternating current power at atime when the frequency of the alternating current power is the firstfrequency and a fourth amplitude of the voltage of the alternatingcurrent power at a time when the frequency of the alternating currentpower is the second frequency.

According to the above aspect, the power transmission control circuitperforms, using the inverter circuit, the amplitude control foreliminating the difference between the third amplitude (V3) of thevoltage of the alternating current power at a time when the frequency ofthe alternating current power is the first frequency and the fourthamplitude (V4) of the voltage of the alternating current power at a timewhen the frequency of the alternating current power is the secondfrequency.

Since almost no difference is left between the amplitude (V3) of thevoltage of the alternating current power at a time when the frequency ofthe alternating current power is the first frequency (f1) and theamplitude (V4) of the voltage of the alternating current power at a timewhen the frequency of the alternating current power is the secondfrequency (f2) as a result of the amplitude control, an incorrectdetermination as in the existing art can be avoided. Even if either thepower transmission apparatus or the power reception apparatus istransmitting data, therefore, the other can transmit data at the sametime. It is to be noted that “eliminating a difference” does not meanthat the difference becomes exactly zero (0), but there may be a slightdifference.

Item 2

The wireless power transmission system according to Item 1,

in which the third amplitude and the fourth amplitude after theamplitude control in the power transmission apparatus correspond toeither the first amplitude or the second amplitude achieved by thevariation performed by the power reception amplitude modulator in thepower reception apparatus.

According to the above aspect, since the third amplitude (V3) and thefourth amplitude (V4) after the amplitude control performed by the powertransmission apparatus correspond to, that is, become the same as,either the first amplitude (V1) or the second amplitude (V2) achieved bythe variation through amplitude modulation performed by the powerreception apparatus, the power transmission apparatus can correctlydetect the second binary communication data transmitted from the powerreception apparatus while transmitting the first binary communicationdata to the power reception apparatus.

Item 3

The wireless power transmission system according to Item 1 or 2,

in which the transmission of the second binary communication data fromthe power reception antenna to the power transmission antenna isperformed at the same time as the transmission of the first binarycommunication data from the power transmission antenna to the powerreception antenna.

According to the above aspect, since the transmission of the firstbinary communication data and the transmission of the second binarycommunication data are simultaneously performed, a delay incommunication can be reduced.

Item 4

The wireless power transmission system according to any of Items 1 to 3,

in which the power transmission apparatus includes an amplitude detectorthat detects amplitude of voltage of the alternating current powertransmitted from the power transmission antenna, and

in which the power reception apparatus includes a frequency detectorthat detects frequency of the alternating current power received by thepower reception antenna.

According to the above aspect, the power transmission apparatus candetect, using the amplitude detector, the second binary communicationdata from the power reception apparatus, and the power receptionapparatus can detect, using the frequency detector, the first binarycommunication data from the power transmission apparatus.

Item 5

The wireless power transmission system according to any of Items 1 to 4,

in which the power transmission control circuit performs, in theamplitude control, control for adjusting the third amplitude of thevoltage of the alternating current power at a time when the frequency ofthe alternating current power is the first frequency to the fourthamplitude of the voltage of the alternating current power at a time whenthe frequency of the alternating current power is the second frequencyon the basis of a result of the detection performed by an amplitudedetection circuit.

According to the above aspect, the power transmission control circuitcan adjust the third amplitude (V3) at a time when the frequency is thefirst frequency to the fourth amplitude (V4) at a time when thefrequency is the second frequency on the basis of a result of thedetection performed by the amplitude detection circuit, incorrectdetection can be prevented during bidirectional communication.

Item 6

The wireless power transmission system according to any of Items 1 to 5,

in which, after performing, in the amplitude control, control foradjusting the third amplitude of the voltage of the alternating currentpower at a time when the frequency of the alternating current power isthe first frequency to the fourth amplitude of the voltage of thealternating current power at a time when the frequency of thealternating current power is the second frequency, the powertransmission control circuit saves a parameter corresponding to adifference in the amplitude of the voltage of the alternating currentpower to a memory.

According to the above aspect, once the control for adjusting the thirdamplitude (V3) to the fourth amplitude (V4) has been performed, next andlater operations of the amplitude control can be performed using theparameter saved in the memory. Processing, therefore, can be performedat higher speed.

Item 7

The wireless power transmission system according to any of Items 1 to 6,

in which the electromagnetic coupling between the power transmissionantenna and the power reception antenna includes magnetic field couplingor electric field coupling.

According to the above aspect, power can be wirelessly transmittedthrough either magnetic field coupling between coils or electric fieldcoupling between electrodes.

Item 8

The wireless power transmission system according to any of Items 1 to 7,

in which the inverter circuit includes four switching elements,

in which the four switching elements include a first switching elementpair that, when conductive, outputs a voltage having the same polarityas voltage of the first direct current power supplied from the powersupply and a second switching element pair that, when conductive,outputs a voltage having an opposite polarity to the voltage of thefirst direct current power,

in which the power transmission control circuit supplies a pulse signalfor switching a conductive/non-conductive state to each of the fourswitching elements, and

in which the amplitude control is performed by adjusting a phasedifference between two pulse signals supplied to the first switchingelement pair and a phase difference between two pulse signals suppliedto the second switching element pair.

According to the above aspect, the amplitude control can be performedthrough simple control for adjusting the phase difference between thetwo pulse signals using a full-bridge inverter circuit.

Item 9

The wireless power transmission system according to any of Items 1 to 8,

in which, after performing, in the amplitude control, control foradjusting the third amplitude of the voltage of the alternating currentpower at a time when the frequency of the alternating current power isthe first frequency to the fourth amplitude of the voltage of thealternating current power at a time when the frequency of thealternating current power is the second frequency, the powertransmission control circuit saves a parameter corresponding to adifference in the amplitude of the voltage of the alternating currentpower to a memory, and

in which the parameter is a value indicating the phase differencesbetween the two pulse signals at a time when the control for adjustingto the fourth amplitude of the voltage of the alternating current powerat a time when the frequency of the alternating current power is thesecond frequency is performed.

According to the above aspect, once the amplitude control has beenperformed, the value saved in the memory indicating the phase differencecan be used in next and later operations. Processing, therefore, can beperformed at higher speed.

Item 10

The wireless power transmission system according to any of Items 1 to 9,

in which the inverter circuit includes a plurality of switchingelements,

in which the power transmission control circuit supplies a pulse signalfor switching a conductive/non-conductive state to each of the pluralityof switching elements, and

in which the amplitude control is performed by adjusting a duty ratio ofthe pulse signals.

According to the above aspect, since the amplitude control can beperformed by adjusting the duty ratio of the pulse signal supplied toeach of the plurality of switching elements, the amplitude control canbe performed not only by a full-bridge inverter but also, for example,by a half-bridge inverter.

Item 11

The wireless power transmission system according to any of Items 1 to10,

in which, after performing, in the amplitude control, control foradjusting the third amplitude of the voltage of the alternating currentpower at a time when the frequency of the alternating current power isthe first frequency to the fourth amplitude of the voltage of thealternating current power at a time when the frequency of thealternating current power is the second frequency, the powertransmission control circuit saves a parameter corresponding to adifference in the amplitude of the voltage of the alternating currentpower to a memory, and

in which the parameter is a value indicating the duty ratio at a timewhen the control for adjusting to the fourth amplitude of the voltage ofthe alternating current power at a time when the frequency of thealternating current power is the second frequency is performed.

According to the above aspect, once the amplitude control has beenperformed, the value saved in the memory indicating the duty ratio canbe used in next and later operations. Processing, therefore, can beperformed at higher speed.

Item 12

A power transmission apparatus in a wireless power transmission systemincluding the power transmission apparatus and a power receptionapparatus, the power transmission apparatus including

an inverter circuit that converts first direct current power suppliedfrom a power supply into alternating current power and outputs thealternating current power,

a power transmission antenna that wirelessly transmits the alternatingcurrent power output from the inverter circuit, and

a power transmission control circuit that causes the inverter circuit tooutput the alternating current power and outputs the alternating currentpower as binary communication data by varying frequency of thealternating current power output from the inverter circuit between afirst frequency and a second frequency,

in which the power reception apparatus includes

a power reception antenna that receives the alternating current powerwirelessly transmitted from the power transmission antenna, and

a power reception amplitude modulator that varies amplitude of voltageof the alternating current power input to the power transmission antennabetween a first amplitude and a second amplitude,

in which, when transmitting first binary communication data from thepower transmission antenna to the power reception antenna throughelectromagnetic coupling between the power transmission antenna and thepower reception antenna, the power transmission control circuit selectsthe first frequency as one of the first binary communication data andthe second frequency as another of the first binary communication data,

in which, when transmitting second binary communication data from thepower reception antenna to the power transmission antenna through theelectromagnetic coupling, the power reception amplitude modulatorselects the first amplitude as one of the second binary communicationdata and the second amplitude as another of the second binarycommunication data, and

in which the power transmission control circuit performs, using theinverter circuit, amplitude control for eliminating a difference betweena third amplitude of the voltage of the alternating current power at atime when the frequency of the alternating current power is the firstfrequency and a fourth amplitude of the voltage of the alternatingcurrent power at a time when the frequency of the alternating currentpower is the second frequency.

The techniques in the present disclosure can be used, for example, fordevices necessary to supply power and transmit bidirectional data inreal-time, such as monitoring cameras and robots. According to theembodiments of the present disclosure, a power transmission apparatusand a power reception apparatus can bidirectionally transmit data in afull-duplex manner.

What is claimed is:
 1. A power reception apparatus comprising: a powerreception antenna that receives alternating current power wirelesslytransmitted, the alternating current power having a first frequency asone of a first binary communication data and a second frequency asanother of the first binary communication data, and a power receptionamplitude modulator that varies amplitude of voltage of the alternatingcurrent power received by the power transmission antenna between a firstamplitude and a second amplitude, wherein, when transmitting secondbinary communication data from the power reception antenna throughelectromagnetic coupling, the power reception amplitude modulatorselects the first amplitude as one of the second binary communicationdata and the second amplitude as another of the second binarycommunication data.
 2. The power reception apparatus according to claim1, wherein the transmission of the second binary communication data fromthe power reception antenna is performed at the same time as thetransmission of the first binary communication data to the powerreception antenna.
 3. The power reception apparatus according to claim1, wherein the power reception apparatus includes a frequency detectorthat detects frequency of the alternating current power received by thepower reception antenna.
 4. The power reception apparatus according toclaim 3, wherein the power reception apparatus includes a powerreception demodulator that demodulates the alternating current power ona basis of the detected frequency to obtain the first binarycommunication data.
 5. The power reception apparatus according to claim1, wherein the electromagnetic coupling includes magnetic field couplingor electric field coupling.
 6. The power reception apparatus accordingto claim 1, wherein the power reception amplitude modulator varies theamplitude of voltage of the alternating current power received by thepower transmission antenna between the first amplitude and the secondamplitude through load modulation.
 7. The power reception apparatusaccording to claim 1, wherein the power reception apparatus includes arectifier that converts the alternating current power into DC power forsupply to a load.
 8. The power reception apparatus according to claim 7,wherein the power reception amplitude modulator varies the amplitude ofvoltage of the alternating current power received by the powertransmission antenna between the first amplitude and the secondamplitude through load modulation, and wherein the power receptionamplitude modulator is connected between the power reception antenna andthe rectifier.
 9. The power reception apparatus according to claim 7,wherein the power reception amplitude modulator varies the amplitude ofvoltage of the alternating current power received by the powertransmission antenna between the first amplitude and the secondamplitude through load modulation, and wherein the power receptionamplitude modulator is connected between the rectifier and the load. 10.A power reception apparatus for a wireless power transmission systemincluding the power transmission apparatus and a power receptionapparatus, the power transmission apparatus comprising: an invertercircuit that converts first direct current power supplied from a powersupply into alternating current power and outputs the alternatingcurrent power; a power transmission antenna that wirelessly transmitsthe alternating current power output from the inverter circuit; and apower transmission control circuit that causes the inverter circuit tooutput the alternating current power and outputs the alternating currentpower as binary communication data by varying frequency of thealternating current power output from the inverter circuit between afirst frequency and a second frequency, wherein the power receptionapparatus includes a power reception antenna that receives thealternating current power wirelessly transmitted from the powertransmission antenna, and a power reception amplitude modulator thatvaries amplitude of voltage of the alternating current power input tothe power transmission antenna between a first amplitude and a secondamplitude, wherein, when transmitting first binary communication datafrom the power transmission antenna to the power reception antennathrough electromagnetic coupling between the power transmission antennaand the power reception antenna, the power transmission control circuitselects the first frequency as one of the first binary communicationdata and the second frequency as another of the first binarycommunication data, wherein, when transmitting second binarycommunication data from the power reception antenna to the powertransmission antenna through the electromagnetic coupling, the powerreception amplitude modulator selects the first amplitude as one of thesecond binary communication data and the second amplitude as another ofthe second binary communication data, and wherein the power transmissioncontrol circuit performs, using the inverter circuit, amplitude controlfor eliminating a difference between a third amplitude of the voltage ofthe alternating current power at a time when the frequency of thealternating current power is the first frequency and a fourth amplitudeof the voltage of the alternating current power at a time when thefrequency of the alternating current power is the second frequency.